Motor Protection Principles.pdf

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Additional <strong>Protection</strong> Methods •Start Inhibit This function will limit starts when the motor is already hot. •Starts/Hour • Time Between Starts (Jogging) • Bearing RTD <strong>Protection</strong> • Acceleration Trip Set higher than the maximum starting time to avoid nuisance tripping when the voltage is lower or for varying loads during acceleration. 34
Conclusions • Induction & synchronous motors are valuable assets to today’s industrial facilities. • The temperature rise of motor dictates its life • When applied, thermal protection can prevent loss of motor life • Additional protection elements such as overvoltage, undervoltage, unbalance, ground fault, differential, short circuit and stator RTD supplement the thermal model protection and provide complete motor protection. • Harsh conformal coating of motor protection relays should be considered to avoid the environmental effects of harsh gaseous sulphides (H2S, etc.) 35
Page 1 and 2: Motor Protection Principles Craig W
Page 3 and 4: Various Industry Motor Applications
Page 5 and 6: Thermal Stress Causes Motor Failure
Page 7 and 8: Motor Electrical Protection • The
Page 9 and 10: Thermal Model - Motor States • Mo
Page 11 and 12: Thermal Overload Pickup • Set to
Page 13 and 14: Overload Curve Selection for Therma
Page 15 and 16: Hot/Cold Safe Stall Ratio HCR = LRT
Page 17 and 18: Overload Curve Selection A custom o
Page 19 and 20: Thermal Model - Current Unbalance B
Page 21 and 22: Thermal Model - RTD Bias • Accele
Page 23 and 24: Overvoltage Protection • The over
Page 25 and 26: Unbalance Protection • Indication
Page 27 and 28: Ground Fault Protection Zero Sequen
Page 29 and 30: Differential Protection • Differe
Page 31 and 32: Differential Protection Biased diff
Page 33: Stator RTD Protection • A simple

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